The Gadsden Purchase Agreement was an agreement between the United States and Mexico in 1854 in which the United States agreed to pay Mexico $10 million for a portion of 29,670 km2 of Mexico, which was later part of Arizona and New Mexico. The purchase of Gadsden provided the necessary land for a southern transcontinental railway and attempted to resolve the conflicts that continued after the war between Mexico and the United States. John Bartlett of Rhode Island, the U.S. negotiator, agreed to allow Mexico to retain the Mesilla Valley (and thus maintain the border at 32-22` N, north of the U.S. claim 31-52` and in the eastern part, also north of the border claimed by Mexico at 32-15 degrees ). 110 W for the Santa Rita Mountains, which were believed to have rich deposits of copper, and some silver and gold that had not yet been extracted. The countries of the South rejected this alternative because of its impact on the railways, but President Fillmore supported it. Southern congressional countries have prevented any approval of the separate border treaty and eliminated other funds for surveying the controversial border country. Robert B. Campbell, an Alabama railroad politician, later replaced Bartlett. Mexico stated that the commissioners` determinations were valid and ready to send troops to enforce the un ratified agreement.  Prior to this treaty, south of the Gila River and west of the Rio Grande was more or less part of Mexico under another agreement, the Treaty of Guadalupe Hidalgo, which officially ended the American war with Mexico in 1848.
If there were to be at a later stage (God forbid) differences of opinion between the two nations that could lead to a breakdown of their relations and reciprocal peace, they would engage in the same way to obtain, by any method, the adjustment of each difference; and if they do not succeed in this way, they will never move on to a declaration of war without first addressing what has been exposed to Article 21 of the Treaty of Guadalupe for similar cases; which article and the twenty-second are confirmed here. The South Pacific portion of Arizona was originally largely in the Gadsden Purchase area, but the western part was later diverted north of the Gila River to serve the City of Phoenix (as part of the EP-SW purchase agreement). The part of New Mexico runs through much of the area that has been the shadow of a controversy between Mexico and the United States after the Guadalupe Hidalgo Treaty came into force and before the purchase of Gadden. In August 1883, the Santa Fe Railroad Company built a railway line via Holbrook, Winslow, Flagstaff and Kingman.  These two transcontinental railways, the Southern Pacific (now part of the Union Pacific Railroad) and the Santa Fe (now part of the BNSF), are among the busiest rail lines in the United States.